User equipment handover method and device

ABSTRACT

Embodiments of the present disclosure describe a user equipment (UE) handover method and a device for the field of wireless communications technologies. The method may include obtaining, by a target base station, an identifier of a source control plane and a context identifier of the UE from a source base station. The method may also include sending, by the target base station, the identifier of the source control plane and the context identifier of the UE to a target control plane device, where the identifier of the source control plane and the context identifier of the UE are used to obtain a context of the UE. Furthermore, for example, an X2-interface-based handover across control planes is provided, and implementation of a core network is simplified.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2016/081030, filed on May 4, 2016, the disclosure of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present application pertains to the field of wireless communicationstechnologies, and in particular, to a user equipment handover method anda device.

BACKGROUND

With rapid development of communications technologies, a Long TermEvolution (LTE) network has been widely used. In the LTE network, when alocation of a user equipment (UE) changes, the UE may be handed overbetween base stations. During a handover, a network side needs to recordlocation information of the UE, so that the UE can be found at any time,and services are provided to a user uninterruptedly. The UE is handedover mainly in two manners: an X2-interface-based handover and anS1-interface-based handover. The two handover manners are based ondifferent interfaces, which means whether a resource preparation processduring a handover is performed by using an X2 interface between the basestations or by using an S1 interface between a base station and amobility management entity (MME). Therefore, if a control plane deviceremains unchanged, either the X2-interface-based handover orS1-interface-based handover may be used; or if the control plane devicechanges, the S1-interface-based handover needs to be used.

In a core network, there are specific constraints for implementation ofthe two handover manners. A control plane device cannot change in theX2-interface-based handover, and the handover can be performed onlybetween eNBs connected to a same control plane device. A control planedevice can change in the S1-interface-based handover; however, moresignaling is to be exchanged between an access network and the corenetwork. In the preceding handover manners, handover modes aredifferent. Consequently, once a handover across control planes isperformed, a handover delay is caused, and handover efficiency isrelatively low.

SUMMARY

Embodiments of the present invention provide a user equipment handovermethod and a device. The technical solutions are as follows:

According to a first aspect, a user equipment UE handover method isprovided, including:

obtaining, by a target base station, an identifier of a source controlplane and a context identifier of the UE from a source base station; andsending, by the target base station, the identifier of the sourcecontrol plane and the context identifier of the UE to a target controlplane device, where the identifier of the source control plane and thecontext identifier of the UE are used to obtain a context of the UE.

According to the technical solution provided in this embodiment of thepresent invention, a target control plane can obtain, from the targeteNB, the ID of the source control plane and the context ID of the UEthat are allocated by the source control plane, to directly request thecontext of the UE from the source control plane, so that the UE ishanded over to a target cell and an X2-interface-based handover acrosscontrol planes is implemented. This implements a unified contextobtaining process in a core network, simplifies core networkimplementation, and reduces a handover delay and improves handoverefficiency during the handover across control planes.

In a first possible embodiment of the first aspect, the obtaining, by atarget base station, an identifier of a source control plane and acontext identifier of UE from a source base station includes:automatically establishing, by the target base station, a connectionbetween the target base station and the source base station, andobtaining, by the target base station, the identifier of the sourcecontrol plane and the context identifier of the UE from the source basestation. After the process of automatically establishing a connectionbetween the base stations, the target eNB can directly interact with thesource eNB, avoiding a process such as forwarding by the core network,and greatly reducing a delay.

Based on any one of the foregoing possible embodiments, in a secondpossible embodiment of the first aspect, the method further includes:

determining, by the target base station based on the identifier of thesource control plane, whether the target base station is connected tothe source control plane; and if the target base station is notconnected to the source control plane, selecting, by the target basestation, a control plane as a target control plane. This provides apossibility for implementation of a handover across control planes.

Based on any one of the foregoing possible embodiments, in a secondpossible embodiment of the first aspect, the method further includes:triggering, by the target base station, release of resources of a sourceside device. The source side device is a device such as a source controlplane device or a source base station. A resource waste of the sourceside device is avoided by monitoring resource release in a timelymanner.

In a third possible embodiment of the first aspect, the triggering, bythe target base station, release of resources of a source side deviceincludes: when the target base station receives a source forwardingplane change flag sent by the target control plane, sending by thetarget base station, a resource release message to the source basestation, where the resource release message carries a source forwardingplane gateway change flag.

Based on any one of the foregoing possible embodiments, in a fourthpossible embodiment of the first aspect, the control plane deviceincludes a mobility management entity or a centralized control planedevice. The method may be applied to a conventional EPC architecture ora CU separation architecture.

According to a second aspect, a user equipment UE handover method isprovided, including: receiving, by a target control plane device, anidentifier of a source control plane and a context identifier of UE thatare sent by a target base station; and obtaining, by the target controlplane device, a context of the UE based on the identifier of the sourcecontrol plane and the context identifier of the UE. Further, the targeteNB determines, based on information such as the identifier, provided bya source eNB, of the source control plane, whether a handover acrosscontrol planes is to be performed; and if a handover across controlplanes is to be performed, selects a new control plane as a targetcontrol plane based on a load status, and sends the identifier of thesource control plane and the context ID of the UE to the target controlplane. The new control plane determines the source control plane basedon the identifier of the source control plane, and obtains the contextof the UE from the source control plane, implementing anX2-interface-based handover method across control planes.

In a first possible embodiment of the second aspect, the obtaining, bythe target control plane device, a context of the UE based on theidentifier of the source control plane and the context identifier of theUE includes:

addressing, by the target control plane device, to the source controlplane based on the identifier of the source control plane, and sending aUE context request message to the source control plane, where the UEcontext request message carries the context identifier of the UE; andreceiving, by the target control plane device, the context of the UEreturned by the source control plane.

In a second possible embodiment of the second aspect, the obtaining, bythe target control plane device, a context of the UE based on theidentifier of the source control plane and the context identifier of theUE includes: obtaining, by the target control plane device, the contextof the UE from a database by using the identifier of the source controlplane and the context identifier of the UE as index information.

In a third possible embodiment of the second aspect, the method furtherincludes: determining, by the target control plane device, whether aforwarding plane gateway needs to change; and if the forwarding planegateway needs to change, sending, by the target control plane device, asource forwarding plane change flag to the target base station, wherethe source forwarding plane change flag is used to trigger release ofresources of a source side device.

In a fourth possible embodiment of the second aspect, the control planedevice includes a mobility management entity or a centralized controlplane device.

According to a third aspect, a wireless communications system isprovided, where the wireless communications system includes at leastuser equipment UE, a source base station, a target base station, asource control plane device, and a target control plane device, where

the target base station is configured to: obtain an identifier of asource control plane and a context identifier of the UE from the sourcebase station, and send the identifier of the source control plane andthe context identifier of the UE to the target control plane device; and

the target control plane device is configured to: receive the identifierof the source control plane and the context identifier of the UE, andobtain a context of the UE based on the identifier of the source controlplane and the context identifier of the UE.

The target base station and the target control plane device in thewireless communications system are further configured to implementeither of the user equipment handover methods in the first aspect andthe second aspect.

According to a fourth aspect, a base station is provided, including aplurality of function modules, configured to implement the userequipment handover method according to any one of the foregoing possibleembodiments of the first aspect.

According to a fifth aspect, a control plane device is provided,including a plurality of function modules, configured to implement theuser equipment handover method according to any one of the foregoingpossible embodiments of the second aspect.

According to a sixth aspect, a base station is provided, where the basestation includes a transmitter, a receiver, a memory, and a processorseparately connected to the transmitter, the receiver, and the memory.Certainly, the base station may further include general purposecomponents such as an antenna, a baseband processing component, anintermediate-frequency processing component, and an input/outputapparatus, and no limitation is imposed thereon in this embodiment ofthe present invention.

The base station is configured to perform the following operations:obtaining an identifier of a source control plane and a contextidentifier of the UE from a source base station; and sending, by thetarget base station, the identifier of the source control plane and thecontext identifier of the UE to a target control plane device, where theidentifier of the source control plane and the context identifier of theUE are used to obtain a context of the UE.

In a first possible embodiment of the sixth aspect, the base station isconfigured to perform the following operations: automaticallyestablishing a connection between the target base station and the sourcebase station, and obtaining the identifier of the source control planeand the context identifier of the UE from the source base station.

Based on any one of the foregoing possible embodiments, in a secondpossible embodiment of the first aspect, the base station is configuredto perform the following operations: determining, based on theidentifier of the source control plane, whether the target base stationis connected to the source control plane; and if the target base stationis not connected to the source control plane, selecting a control planeas a target control plane.

Based on any one of the foregoing possible embodiments, in a secondpossible embodiment of the first aspect, the base station is configuredto perform the following operation: triggering release of resources of asource side device.

In a third possible embodiment of the sixth aspect, the base station isconfigured to perform the following operation: when a source forwardingplane change flag sent by the target control plane is received, sendinga resource release message to the source base station, where theresource release message carries a source forwarding plane gatewaychange flag.

Based on any one of the foregoing possible embodiments, in a fourthpossible embodiment of the sixth aspect, the control plane deviceincludes a mobility management entity or a centralized control planedevice.

According to a seventh aspect, a control plane device is provided, wherethe control plane device includes a transmitter, a receiver, a memory,and a processor separately connected to the transmitter, the receiver,and the memory. Certainly, the control plane device may further includegeneral purpose components such as an antenna, a baseband processingcomponent, an intermediate-frequency processing component, and aninput/output apparatus, and no limitation is imposed thereon in thisembodiment of the present invention.

The control plane device is configured to perform the followingoperations: receiving an identifier of a source control plane and acontext identifier of UE that are sent by a target base station; andobtaining a context of the UE based on the identifier of the sourcecontrol plane and the context identifier of the UE.

In a first possible embodiment of the seventh aspect, the control planedevice is configured to perform the following operations: addressing tothe source control plane based on the identifier of the source controlplane; sending a UE context request message to the source control plane,where the UE context request message carries the context identifier ofthe UE; and receiving the context of the UE returned by the sourcecontrol plane.

In a second possible embodiment of the seventh aspect, the control planedevice is configured to perform the following operation: obtaining thecontext of the UE from a database by using the identifier of the sourcecontrol plane and the context identifier of the UE as index information.

In a third possible embodiment of the seventh aspect, the control planedevice is configured to perform the following operations: determiningwhether a forwarding plane gateway needs to change; and if theforwarding plane gateway needs to change, sending a source forwardingplane change flag to the target base station, where the sourceforwarding plane change flag is used to trigger release of resources ofa source side device.

In a fourth possible embodiment of the seventh aspect, the control planedevice includes a mobility management entity or a centralized controlplane device.

It should be understood that, the foregoing general description and thefollowing detailed description are merely an example and aninterpretation, and are not intended to limit the present invention.

BRIEF DESCRIPTION OF DRAWINGS

The drawings herein are incorporated in this specification andconstitute a part of this specification, show embodiments conforming tothe present invention, and explain principles of the present inventiontogether with this specification.

FIG. 1 is a schematic diagram of a conventional evolved packet core(EPC) network architecture;

FIG. 2 is a schematic diagram of a self-organizing network (SON) basedon a conventional EPC network architecture;

FIG. 3 is an interaction flowchart of a UE handover method based on theconventional EPC network architecture shown in FIG. 1;

FIG. 4A and FIG. 4B are an interaction flowchart of another UE handovermethod based on the conventional EPC network architecture shown in FIG.1;

FIG. 5 is a schematic diagram of a control and user plane (CU)separation network architecture;

FIG. 6 is an interaction flowchart of a UE handover method based on theCU separation network architecture shown in FIG. 5;

FIG. 7A and FIG. 7B are an interaction flowchart of another UE handovermethod based on the CU separation network architecture shown in FIG. 5;

FIG. 8 is a schematic structural diagram of a base station according toan embodiment of the present invention;

FIG. 9 is a schematic structural diagram of a control plane deviceaccording to an embodiment of the present invention;

FIG. 10 is a schematic structural diagram of a base station according toan embodiment of the present invention; and

FIG. 11 is a schematic structural diagram of a control plane deviceaccording to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Example embodiments are described in detail herein, and examples of theexample embodiments are presented in the accompanying drawings. When thefollowing description relates to the accompanying drawings, unlessspecified otherwise, same numbers in different accompanying drawingsrepresent a same or similar element. Implementations described in thefollowing example embodiments do not represent all implementationsconsistent with the present invention. On the contrary, they are onlyexamples of apparatuses and methods that are described in the appendedclaims in detail and that are consistent with some aspects of thepresent invention.

In the following, a conventional EPC network architecture shown in FIG.1 is used as an example to briefly describe some devices used in theembodiments of the present invention:

Mobility management entity (MME): The MME is responsible for usermobility management, including user context and mobile state management,user temporary identity allocation, and user authentication andauthorization.

Serving gateway (SGW): The SGW is a forwarding plane anchor betweenthird generation partnership project (3GPP) access networks; forwardspackets of UEs through transmission tunnels between the SGW and a basestation and between the SGW and a packet data network gateway (P-GW); isresponsible for bearer establishment, modification, and release, andquality of service (QoS) control, and supports main QoS parameters of abearer, including a QoS class identifier (QCI), an address resolutionprotocol (ARP), and a guaranteed bit rate (GBR); and is responsible forstoring information such as an evolved packet switched system (EPS)bearer context including a tunnel identifier and a user identity.

Packet data network gateway (PGW): The PGW is a forwarding plane anchorbetween a 3GPP access network and a non-3GPP access network, and is aninterface between the 3GPP access network and an external packet datanetwork (PDN). The PGW may be integrated with the SGW, and isresponsible for IP address allocation; bearer establishment,modification, and release; selection of a policy and charging rulesfunction (PCRF) unit; QoS control; implementation of a policy andcharging enforcement function; and storage of an EPS bearer contextincluding a tunnel identifier and a user identity.

eNB: The eNB is configured to: (1) implement a radio resource managementrelated function, including radio bearer control; (2) transmit a pagingmessage, where: after receiving a paging message from a control plane,the eNB sends the paging message to an air interface; and (3) during ahandover, determine the handover and prepare resources required for thehandover.

Gateway user plane (GW-U): The GW-U has functions such as forwarding,encapsulation, and statistics collection of a user packet.

Control plane (Controller): The control plane integrates functions ofdevices such as the MME and a gateway control plane, is responsible foruser mobility management, and further has functions such as IP addressallocation, selection of a gateway user plane device, bearer management,and generation of a gateway user plane forwarding rule.

To help an LTE operator better manage a huge quantity of base stationsthat may be provided by different device vendors in a network, reduceoperating expenses, and reduce human participation, a concept of selforganized network (SON) has been proposed. A main idea of the SON is toimplement some autonomous functions of a wireless network. The SONmainly includes three functions: self-configuration, self-optimization,and self-healing. The self-configuration function includes automaticallyobtaining an IP address and configuring an automatic neighbor relation.Automatically obtaining an IP address means that an eNB automaticallyobtains an IP address after being powered on, and obtains IP addressesof a network management system and an access gateway. Configuring anautomatic neighbor relation means that during automatic establishment,an eNB establishes an automatic neighbor relation by using a neighborrelation list delivered by the network. After entering a working state,the eNB optimizes the automatic neighbor relation, reducing labor costsof optimization and planning.

eNB automatic establishment is one of most basic functions of the SON.According to a standard protocol, when accessing the network, a new eNBcan automatically establish an IP connection between the eNB and anelement management (EM), and can automatically download software, awireless parameter, and data related to transmission configuration. X2interfaces can be automatically established. After the establishment iscomplete, the eNB may check the working state of the eNB and report acheck result to a network management center.

FIG. 2 is a system architecture diagram according to an embodiment ofthe present invention. Referring to FIG. 2, a system includes a sourceMME, a target MME, a source SGW, a target SGW, and a PGW, and furtherincludes a plurality of eNBs. Certainly, the system should furtherinclude devices such as UE, which are not shown in the figure.

It should be noted that a source eNB is an eNB connected before alocation of UE changes, and a target eNB is an eNB selected by the UEafter the location changes and the source eNB determines that a handoveris required.

An X2 interface is provided between eNBs connected to a same MME, and anS1 interface is provided between the MME and an eNB. Through aself-configuration process of an eNB supporting a SON, an IP address canbe automatically obtained, and an X2 interface between eNBs connected todifferent MMES can be configured. In this way, eNBs connected todifferent MMEs can directly interact with each other by using anautomatically configured X2 interface, to implement an X2-basedhandover. During the X2-based handover, a source eNB automaticallyobtains an address of a target eNB without participation of a corenetwork, and the eNBs may be controlled by different control planedevices.

FIG. 3 is an interaction flowchart of a UE handover method according toan embodiment of the present invention. An interaction process in FIG. 3is performed based on the system architecture shown in FIG. 1, and isused to describe an interaction scenario in which an SGW remainsunchanged. Specifically, this embodiment includes the following steps.

300. A source eNB performs X2-interface-based connection to a target eNBthrough SON automatic configuration.

Herein, a decision-making process during a handover is not described indetail. How UE specifically reports a measurement report and how thesource eNB determines, based on the measurement report or otherinformation of the UE, whether to perform a handover or what kind ofhandover is to be performed are not limited in this embodiment of thepresent invention.

During handover preparation, the source eNB makes a handover decision todetermine which eNB is used as the target eNB to perform a handover. Ifthe source eNB does not store an IP address of the target eNB, it ispossible that the source eNB and the target eNB are not connected to asame MME. In this case, step 300 needs to be performed to automaticallyconfigure an X2 interface between the eNBs.

301. The source eNB sends a handover request message to the target eNB,where the handover request message carries a GUMMEI and an MME UE S1APID of a source MME.

Further, if determining, based on the GUMMEI of the source MME, that thetarget eNB is not connected to the source MME, the target eNB selects,based on a load status, a new MME to perform a handover.

Selecting an MME based on the load status means that the target eNodeBneeds to select an MME pool to serve the UE. There are many MMEs in anMME pool. The eNodeB selects an MME pool based on a network topology andan average load of the MME pool, so that a probability of changing aserving MME when the UE moves subsequently is reduced.

302. When receiving the handover request message, the target eNB sends apath switch request message to a target MME.

The path switch request message includes a cell global identifier(tracking area identity (TAI)+E-UTRAN cell global identifier (ECGI)) ofa target cell, a converted EPS bearer list, UE security capabilities, aclosed user group ID (Closed Subscriber Group Identity, CSG ID), and acell access mode (CAM). Different from that in the prior art, the pathswitch request message further includes an identifier of the sourcecontrol plane, namely a globally unique MME identifier (GUMMEI), and auser context identifier UE S1AP ID (user context identifier) of thesource MME. A context of the UE can be obtained from the source MMEbased on the source MME GUMMEI (control plane identifier) and the usercontext identifier UE S1AP ID of the source MME that are carried in thepath switch request message.

A GUMMEI is a part of a globally unique temporary identity (GUTI), andmay be used to uniquely identify an MME that allocates the GUTI. An MMEUE S1AP ID is used by an MME to uniquely identify UE on an S1 interface.

303. When receiving the path switch request message sent by the targeteNB, the target MME queries a context of UE locally based on the UE S1APID of the source MME.

When receiving the path switch request message sent by the target eNB,the target MME may learn that a handover event is requested to beperformed, and therefore may first attempt to locally query the contextof the UE.

304. When failing to obtain the context of the UE locally through query,the target MME sends a UE context request message to the source MMEindicated by the source MME GUMMEI, where the UE context request messagecarries the UE S1AP ID of the source MME.

Step 304 may include a process in which the target MME addresses to thesource control plane based on the identifier of the source control planeand sends the UE context request message to the source MME.

305. When receiving the UE context request message, the source MMEqueries the context of the UE locally based on the UE S1AP ID of thesource MME.

The context of the UE includes an IMSI, a UE core network capability, aTA list, an ID of a cell, on a source side, on which the UE camps, anaddress and a TEID of an SGW/PGW on an S11 interface, a PDN type, an EPSbearer identifier, and an access point name (APN) of a user, QoS of adefault EPS bearer, and the like. The S11 interface is an interfacebetween an MME and an SGW.

306. The source MME sends the context of the UE to the target MME.

307. After the source MME sends the context of the UE to the target MME,the source MME starts a timer to monitor when to release UE resourcesstored by the source eNB and locally stored UE resources.

308. After receiving the context of the UE, the target MME determines,based on the context of the UE and the target cell ID, whether to changean SGW.

The target MME may determine, based on the address, carried in thecontext of the UE, of the SGW/PGW on the S11 interface and the targetcell ID, whether a path between the SGW and the target cell is anoptimized path. If the path is an optimized path, it may be determinednot to change the SGW. If the path is not an optimized path, it may bedetermined to change the SGW.

309. If determining not to change the SGW, the target MME sends asession creation request message to the SGW.

The address of the SGW on the S11 interface can be obtained in step 305.Therefore, in step 309, the session creation request message may be sentto the SGW based on the address obtained in step 305. The sessioncreation request message includes a to-be-established EPS bearer, theAPN of the user, an address and a TEID, on a user plane, of the targeteNB, and the like.

310. The SGW/PGW sends a session creation response message to the targetMME.

In the scenario of FIG. 3, neither the SGW nor the PGW has changed.

311. When the target MME receives the session creation response message,the target MME sends a path switch request response message to thetarget eNB.

The path switch request response message includes an address and a TEIDthat are allocated on the user plane by the SGW for uplink data.

312. After the timer expires, the source MME sends a resource releasemessage to the source eNB, to instruct the source eNB to release locallystored UE resources.

Further, when the timer expires, the source MME may also release UEresources locally stored by the source MME.

313. The target MME implements a handover process based on the contextof the UE.

The specific handover process may include a process in which the targetMME synchronizes the UE to the target cell based on the context of theUE, and the like. No further details are provided in this embodiment ofthe present invention.

The embodiment shown in FIG. 3 provides a handover method performed in ascenario in which an SGW does not need to change. However, during ahandover, to optimize a routing path, or when there is no interface toconnect a source SGW and a target MME, an SGW may change. FIG. 4A andFIG. 4B are an interaction flowchart of a handover method according toan embodiment of the present invention, and is used to describe aninteraction scenario in which an SGW changes. Specifically, thisembodiment includes the following steps.

400. A source eNB performs X2-interface-based connection to a targetside eNB through SON automatic configuration.

Step 400 is similar to step 300, and is not described herein again.

401. The source eNB sends a handover request message to the target eNB,where the handover request message carries a GUMMEI and an MME UE S1APID of a source MME.

402. The target eNB sends a path switch request message to a target MME.

403. When receiving the path switch request message sent by the targeteNB, the target MME queries a context of UE locally based on the UE S1APID of the source MME.

404. When failing to obtain the context of the UE locally through query,the target MME sends a UE context request message to the source MMEindicated by the source MME GUMMEI, where the UE context request messagecarries the UE S1AP ID of the source MME.

405. When receiving the UE context request message, the source MMEqueries the context of the UE locally based on the UE S1AP ID of thesource MME.

406. The source MME sends the context of the UE to the target MME.

407. After receiving the context of the UE, the target MME determines tochange an SGW.

408. The target MME sends a UE context response message to the sourceMME, where the UE context response message carries an SGW change flag.

409. When receiving the UE context response message of the target MME,the source MME learns that the SGW changes on the target MME side, andstarts a timer to monitor when to release UE resources stored by thesource eNB and UE resources stored by the source SGW.

In steps 407 and 408, the target MME may determine to change the SGW tooptimize a routing path or when there is no interface to connect thesource SGW and the target MME, and therefore needs to inform the sourceMME of the SGW change.

410. The target MME sends a session creation request message to a targetSGW, where the session creation request message includes an address anda TED of the target eNB, a bearer context, an address and a TED of aPGW, and the like that are used on a user plane.

411. After receiving the session creation request message, the targetSGW sends a bearer modification request message to the PGW based on thereceived PGW address, where the bearer modification request messageincludes an address and a TED of the SGW that are allocated by thetarget SGW for downlink data.

412. When receiving the bearer modification request message, the PGWsends a bearer modification response message to the target SGW, wherethe bearer modification response message includes an address and a TEIDof the PGW that are allocated by the PGW for uplink data.

In addition, the bearer modification response message may furtherinclude a charging ID, which is used by the PGW to charge a packet.

413. After receiving the bearer modification response message, thetarget SGW sends a session creation response message to the target MME,where the session creation response message includes an address and aTEID that are allocated, on the user plane, by the target SGW for theuplink data.

414. The target MME sends a path switch request response message to thetarget eNB, where the path switch request response message includes theaddress and the TED that are allocated, on the user plane, by the targetSGW for the uplink data.

415. When the timer of the source MME expires, the source MME sends aresource release message to the source eNB.

416. When receiving the resource release message, the source eNBreleases UE resources.

The UE resources may include radio bearers of the UE and all controlplane resources related to the context of the UE.

417. The source MME sends a session deletion request message to thesource SGW, where the session deletion request message is used torelease the UE resources stored by the source SGW.

The embodiments of FIG. 3 and FIG. 4A and FIG. 4B separately describe aUE handover process in the conventional EPC network architecture. Thetarget MME may obtain, from the target eNB, the ID of the source controlplane and the context ID of the UE that are allocated by the source MME,to directly request the context of the UE from the source MME, so thatthe UE is handed over to the target cell and an X2-interface-basedhandover across control planes is implemented. This implements a unifiedcontext obtaining process in a core network, simplifies core networkimplementation, and reduces a handover delay and improves handoverefficiency during the handover across control planes.

Further, the target eNB determines, based on information such as theidentifier, provided by the source eNB, of the source control plane,whether a handover across MMEs is to be performed; and if a handoveracross MMEs is to be performed, selects a new MME as a target MME basedon a load status, and sends the identifier of the source control planeand the context ID of the UE to the target MME. The new MME determinesthe source MME based on the identifier of the source control plane, andobtains the context of the UE from the source MME, implementing anX2-interface-based handover method across control planes.

FIG. 5 is an architectural diagram of a CU separation mobile networksystem according to an embodiment of the present invention. A CUseparation network architecture decouples a control plane function of amobile gateway from a forwarding plane function of the mobile gateway,and combines the separated control plane function (GW-C) withconventional 3GPP control network elements such as an MME and a PCRFinto a unified control plane. A forwarding plane GW-U includes aforwarding plane (SGW-U) of an S-GW and a forwarding plane (PGW-U) of aP-GW. Referring to FIG. 5, the system includes a source control planedevice, a target control plane device, a source GW-U, a target GW-U, anSDN control device, and the like, and further includes a plurality ofeNBs. Certainly, the system should further include devices such as UE,which are not shown in the figure. Different from the architecture shownin FIG. 1, the system shown in FIG. 5 further includes a database (asshown in a dashed-line box in the figure). After UE accesses a network,the control plane Controller synchronizes a context of the UE to thedatabase, so that the database can centrally manage contexts.

Neighboring eNBs in the system can automatically establish an X2interface by using a SON. During handover preparation, a source eNBmakes a handover decision to determine which target eNB to be handedover to. If the source eNB does not store an IP address of the targeteNB, the source eNB automatically establishes an X2-interface-basedconnection to the target side eNB through SON automatic configuration.

Then, the source eNB sends a handover request message, which carries anID of the source controller, to the target eNB; and if the target eNB isnot connected to the source controller, selects, based on a load status,a new controller to perform a handover. The target eNB needs to placethe source control plane identifier ID and a user context identifier IDin a path switch request message, so that the target controller obtainsthe context of the UE from the source controller. Then, the targetcontroller synchronizes the UE to a target cell based on the context ofthe UE, and completes a handover process.

FIG. 6 shows a handover process in a CU separation mobile networkarchitecture. After a control plane is separated from a user plane, aGW-U is connected to only one controller. Therefore, a GW-U changedefinitely occurs in a handover across controllers. In this case, anembodiment of a handover method applicable to a scenario in which a GW-Uchanges is provided. A specific process is shown in FIG. 6.

600. A source eNB performs X2-interface-based connection to a target eNBthrough SON automatic configuration.

Step 600 is similar to step 300, and is not described herein again.

601. The source eNB sends a handover request message to the target eNB,where the handover request message carries a source controller ID and auser context identifier UE S1AP ID of a source controller.

602. The target eNB sends a path switch request message to a targetcontroller.

The path switch request message includes a cell global identifier(TAI+ECGI) of a target cell, a converted EPS bearer list, UE securitycapabilities, a CSG ID, and a cell access mode. Different from that inthe prior art, the path switch request message further includes thesource controller ID (control plane identifier) and the user contextidentifier UE S1AP ID (user context identifier) of the sourcecontroller. A context of UE can be obtained from the source controllerbased on the source controller ID (control plane identifier) and theuser context identifier UE S1AP ID (user context identifier) of thesource controller that are carried in the path switch request message.

The source controller ID uniquely identifies the source control plane,and the UE S1AP ID is used by the controller to uniquely identify the UEon an S1 interface.

603. When receiving the path switch request message sent by the targeteNB, the target controller queries a context of UE locally based on theUE S1AP ID of the source controller.

604. When failing to obtain the context of the UE locally through query,the target controller sends a UE context request message to the sourcecontroller indicated by the source controller ID, where the UE contextrequest message carries the UE S1AP ID of the source controller.

605. When receiving the UE context request message, the sourcecontroller queries the context of the UE locally based on the UE S1AP IDof the source controller.

606. The source controller sends the context of the UE to the targetcontroller.

607. After receiving the context of the UE, the target controller sendsa UE context response message to the source controller, where the UEcontext response message carries a GW-U change flag.

After obtaining the context of the UE, the target controller maydetermine, based on a location of a cell on which the UE camps before ahandover and a location of a target cell, whether to change a forwardingplane gateway. If it is determined to change the forwarding planegateway, the target controller may trigger a resource release process ofa source side device, and implement a process of sending the UE contextresponse message in step 607 to inform the source controller of a GW-Uchange, so that the source controller monitors release of source sideresources.

608. When receiving the UE context response message of the targetcontroller, the source controller learns that a GW-U changes on thetarget controller side, and starts a timer to monitor when to release UEresources stored by the source eNB and UE resources stored by the sourceGW-U.

609. After the target controller receives the context of the UE, thetarget controller sends a downlink data forwarding rule to a target GW-Uto instruct the gateway forwarding plane how to process an IP packetsent by the UE.

610. The target controller sends a path switch response message to thetarget eNB.

611. When the timer of the source controller expires, the sourcecontroller sends a resource release message to the source eNB.

Further, when the timer expires, the source controller may also releaseUE resources locally stored by the source controller.

612. When receiving the resource release message, the source eNBreleases UE resources.

613. The source controller sends a resource release message to thesource GW-U.

614. When receiving the resource release message, the source GW-Ureleases UE resources.

It should be noted that step 611 and step 613 may be performed at a sametime, or may be performed one after another. An actual sequence forperforming step 611 and step 613 is not limited in this embodiment ofthe present invention, provided that the source side devices canseparately release the UE resources when the timer of the sourcecontroller expires.

The UE context in the embodiment shown in FIG. 6 is sent by the sourcecontroller to the target controller. In another embodiment, a UE contextmay alternatively be obtained from a database, as shown in FIG. 7A. WhenUE accesses a network, any controller, such as the source controller inthis embodiment, updates a locally cached context of the UE to thedatabase in real time. The database centrally manages contexts stored bythe control plane, and can implement functions such as dynamic resourcemigration and disaster recovery backup.

700. A source eNB performs X2-interface-based connection to a target eNBthrough SON automatic configuration.

Step 700 is similar to step 300, and is not described herein again.

701. The source eNB sends a handover request message to the target eNB,where the handover request message carries a source controller ID and auser context identifier UE S1AP ID of a source controller.

702. The target eNB sends a path switch request message to a targetcontroller.

Further, if the target eNB is not connected to the source controller, anew controller is selected based on a load status to perform a handover,and the selected controller is the target controller.

The path switch request message includes a cell global identifier(TAI+ECGI) of a target cell, a converted EPS bearer list, UE securitycapabilities, a CSG ID, and a cell access mode. Different from that inthe prior art, the path switch request message further includes thesource controller ID (control plane identifier) and the user contextidentifier UE S1AP ID (user context identifier) of the sourcecontroller. The context of the UE can be obtained from the sourcecontroller based on the source controller ID (control plane identifier)and the user context identifier UE S1AP ID (user context identifier) ofthe source controller that are carried in the path switch requestmessage.

The source controller ID uniquely identifies the source control plane,and the UE S1AP ID is used by the controller to uniquely identify the UEon an S1 interface.

703. When receiving the path switch request message sent by the targeteNB, the target controller queries a context of the UE locally based onthe UE S1AP ID of the source controller.

Before the UE is moved to the target cell, the database predicts, basedon a movement track or a location of the UE, a range of areas to whichthe UE may move, and proactively pushes the context of the UE to thetarget controller. If the context of the UE cannot be obtained throughquery in step 703, the previous intelligent pushing by the databasefails, and the context information of the UE needs to be obtained fromthe database by using the source controller ID and the UE S1AP ID of thesource controller that are obtained previously.

704. When failing to obtain the context of the UE locally through query,the target controller sends a UE context request message to thedatabase, where the UE context request message carries the sourcecontroller ID and the UE S1AP ID of the source controller.

705. When receiving the UE context request, the database queries thecontext of the UE in the database.

The context of the UE includes an IMSI, a UE core network capability, aTA list, an ID of a cell, on a source side, on which the UE camps, anEPS bearer identifier, an APN of a user, QoS of a default EPS bearer,and the like.

706. The database sends the context of the UE to the target controller.

Steps 704 to 706 are a process in which the target control plane deviceobtains the context of the UE from the database by using the sourcecontrol plane identifier and the context identifier of the UE as indexinformation.

707. After the target controller receives the context of the UE, thetarget controller sends a downlink data forwarding rule to a target GW-Uto instruct the gateway forwarding plane how to process an IP packetsent by the UE.

After obtaining the context of the UE, the target controller maydetermine, based on a location of a cell on which the UE camps before ahandover and a location of the target cell, whether to change aforwarding plane gateway. If it is determined to change the forwardingplane gateway, the target controller may trigger a resource releaseprocess of a source side device by using the target eNB.

708. The target controller sends a path switch request response messageto the target eNB, where the path switch request response messagecarries a GW-U change flag.

A sequence for performing step 707 and step 708 is not limited in thisembodiment of the present invention.

709. After receiving the path switch request response message, thetarget eNB sends a resource release message to the source eNB, where theresource release message carries the GW-U change flag.

710. After receiving the resource release message, the source eNB sendsthe resource release message to the source controller, where theresource release message carries the GW-U change flag.

711. The source controller sends the resource release message to thesource GW-U.

712. When receiving the resource release message, the source GW-Ureleases UE resources.

The source controller sends the resource release message to the sourceGW-U because of a GW-U change.

The embodiments of FIG. 6 and FIG. 7A and FIG. 7B separately describe aUE handover process in the CU network architecture. The targetcontroller may obtain, from the target eNB, the source control plane IDand the UE context ID that are allocated by the source controller, todirectly request the context of the UE from the source controller, orthe context of the UE is synchronized to the target controller by usingthe database. In this way, an X2-interface-based handover across controlplanes is implemented, reducing a control plane delay and improvinghandover efficiency.

Further, compared with a prior-art X2-interface-based handover, duringthe prior-art X2-based handover, after a target eNB obtains source sideinformation from an X2 interface and finds that a source control planeand the target eNB are not connected, the target eNB rejects theX2-based handover, and therefore a process of selecting a new controlplane is not triggered. In other words, a handover across control planescannot be performed during the prior-art X2-interface-based handover.However, in the embodiments of the present invention, the target eNBdetermines, based on information such as the source control planeidentifier provided by the source eNB, whether a handover acrosscontrollers is to be performed; and if a handover across controllers isto be performed, selects a new controller as a target controller basedon the load status, and sends the source control plane identifier andthe UE context ID to the target controller. The target controller mayobtain the context of the UE from the source controller based on thesource control plane identifier, or synchronizes the context of the UEto the target controller by using the database, implementing anX2-interface-based handover method across control planes.

The following are apparatus embodiments of the present invention, andapparatuses may be used to implement the method embodiments of thepresent invention. For details not disclosed in the apparatusembodiments of the present invention, refer to the method embodiments ofthe present invention.

FIG. 8 is a schematic structural diagram of a base station according toan embodiment of the present invention. Referring to FIG. 8, the basestation includes:

an obtaining module 801, configured to obtain an identifier of a sourcecontrol plane and a context identifier of the UE from a source basestation; and

a sending module 802, configured to send the identifier of the sourcecontrol plane and the context identifier of the UE to a target controlplane device, where the identifier of the source control plane and thecontext identifier of the UE are used to obtain a context of the UE.

In a possible embodiment, the obtaining module 801 is configured toautomatically establish a connection between the target base station andthe source base station, and the target base station obtains theidentifier of the source control plane and the context identifier of theUE by using the source base station.

In a possible embodiment, the base station further includes a selectionmodule, configured to: determine, based on the identifier of the sourcecontrol plane, whether the target base station is connected to thesource control plane; and if the target base station is not connected tothe source control plane, select a control plane as a target controlplane.

In a possible embodiment, the base station further includes a releasemodule, configured to trigger release of resources of a source sidedevice.

In a possible embodiment, the release module is configured to: when asource forwarding plane change flag sent by the target control plane isreceived, send a resource release message to the source base station,where the resource release message carries a source forwarding planegateway change flag.

It should be noted that when the base station provided in the foregoingembodiment implements a user equipment handover function, description isprovided only by using division of the foregoing function modules as anexample. In actual application, the functions may be allocated todifferent function modules for implementation depending on actualrequirements. To be specific, an internal structure of the device isdivided into different function modules to implement all or part of thefunctions described above. For the apparatus in the foregoingembodiment, specific manners of performing operations by each module aredescribed in detail in the embodiments related to the method, and nodetails are repeated herein.

FIG. 9 is a schematic structural diagram of a control plane deviceaccording to an embodiment of the present invention. Referring to FIG.9, the control plane device includes:

a receiving module 901, configured to receive an identifier of a sourcecontrol plane and a context identifier of UE that are sent by a targetbase station; and

an obtaining module 902, configured to obtain a context of the UE basedon the identifier of the source control plane and the context identifierof the UE.

In a possible embodiment, the obtaining module 902 is configured to:address to the source control plane based on the identifier of thesource control plane; send a UE context request message to the sourcecontrol plane, where the UE context request message carries the contextidentifier of the UE; and receive the context of the UE returned by thesource control plane.

In a possible embodiment, the obtaining module 902 is configured toobtain the context of the UE from a database by using the identifier ofthe source control plane and the context identifier of the UE as indexinformation.

In a possible embodiment, the control plane device further includes:

a determining module, configured to determine whether a forwarding planegateway needs to change; and

a sending module, configured to: if the determining module determinesthat the forwarding plane gateway needs to change, send a sourceforwarding plane change flag to the target base station, where thesource forwarding plane change flag is used to trigger release ofresources of a source side device.

In a possible embodiment, the control plane device includes a mobilitymanagement entity or a centralized control plane device.

It should be noted that when the control plane device provided in theforegoing embodiment implements a user equipment handover function ofthe control plane device, description is provided only by using divisionof the foregoing function modules as an example. In actual application,the functions may be allocated to different function modules forimplementation depending on actual requirements. To be specific, aninternal structure of the device is divided into different functionmodules to implement all or part of the functions described above. Forthe apparatus in the foregoing embodiment, specific manners ofperforming operations by each module are described in detail in theembodiments related to the method, and no details are repeated herein.

Referring to FIG. 10, FIG. 10 is a schematic structural diagram of abase station according to an embodiment of the present invention. Asshown in the figure, the base station includes a transmitter, areceiver, a memory, and a processor separately connected to thetransmitter, the receiver, and the memory. Certainly, the base stationmay further include general purpose components such as an antenna, abaseband processing component, an intermediate-frequency processingcomponent, and an input/output apparatus, and no limitation is imposedthereon in this embodiment of the present invention.

The base station is configured to perform the user equipment handovermethod on a base station side provided in any embodiment in FIG. 3, FIG.4A and FIG. 4B, FIG. 6, or FIG. 7A and FIG. 7B.

The transmitter and the receiver may alternatively be a transceiver. Theprocessor may be a central processing unit (CPU), a microprocessor, asingle-chip microcomputer, or the like.

Referring to FIG. 11, FIG. 11 is a schematic structural diagram of acontrol plane device according to an embodiment of the presentinvention. As shown in the figure, the control plane device includes atransmitter, a receiver, a memory, and a processor separately connectedto the transmitter, the receiver, and the memory. Certainly, the controlplane device may further include general purpose components such as anantenna, a baseband processing component, an intermediate-frequencyprocessing component, and an input/output apparatus, and no limitationis imposed thereon in this embodiment of the present invention.

The control plane device is configured to perform the user equipmenthandover method on a control plane device side provided in anyembodiment in FIG. 3, FIG. 4A and FIG. 4B, FIG. 6, or FIG. 7A and FIG.7B.

A person skilled in the art can easily figure out another implementationsolution of the present invention after considering the specificationand practicing the present invention disclosed herein. This applicationis intended to cover any variations, functions, or adaptive changes ofthe present invention. These variations, functions, or adaptive changescomply with general principles of the present invention, and includecommon knowledge or a commonly used technical means in the technicalfield that is not disclosed in the present invention. The specificationand the embodiments are merely considered as examples, and the actualscope and the spirit of the present invention are pointed out by thefollowing claims.

It should be understood that the present invention is not limited to theaccurate structures that are described in the foregoing and that areshown in the accompanying drawings, and modifications and changes may bemade without departing from the scope of the present invention. Thescope of the present invention is limited only by the appended claims.

1. A user equipment (UE) handover method, comprising: obtaining, by atarget base station, an identifier of a source control plane and acontext identifier of a UE from a source base station; and sending, bythe target base station, the identifier of the source control plane andthe context identifier of the UE to a target control plane device,wherein the identifier of the source control plane and the contextidentifier of the UE are used to obtain a context of the UE.
 2. Themethod according to claim 1, wherein the obtaining, by the target basestation, the identifier of the source control plane and the contextidentifier of the UE from the source base station comprises:automatically establishing, by the target base station, a connectionbetween the target base station and the source base station, andobtaining, by the target base station, the identifier of the sourcecontrol plane and the context identifier of the UE from the source basestation.
 3. The method according to claim 1, wherein the method furthercomprises: determining, by the target base station based on theidentifier of the source control plane, whether the target base stationis connected to the source control plane; and when the target basestation is not connected to the source control plane, selecting, by thetarget base station, a control plane as a target control plane.
 4. Themethod according to claim 1, wherein the method further comprises:triggering, by the target base station, release of resources of a sourceside device.
 5. The method according to claim 4, wherein the triggering,by the target base station, release of resources of a source side devicecomprises: when the target base station receives a source forwardingplane change flag sent by the target control plane, sending by thetarget base station, a resource release message to the source basestation, wherein the resource release message carries a sourceforwarding plane gateway change flag.
 6. The method according to claim1, wherein the control plane device comprises a mobility managemententity or a centralized control plane device.
 7. A user equipment (UE)handover method, comprising: receiving, by a target control planedevice, an identifier of a source control plane and a context identifierof a UE that are sent by a target base station; and obtaining, by thetarget control plane device, a context of the UE based on the identifierof the source control plane and the context identifier of the UE.
 8. Themethod according to claim 7, wherein the obtaining, by the targetcontrol plane device, the context of the UE based on the identifier ofthe source control plane and the context identifier of the UE comprises:addressing, by the target control plane device, to the source controlplane based on the identifier of the source control plane, and sending aUE context request message to the source control plane, wherein the UEcontext request message carries the context identifier of the UE; andreceiving, by the target control plane device, the context of the UEreturned by the source control plane.
 9. The method according to claim7, wherein the obtaining, by the target control plane device, thecontext of the UE based on the identifier of the source control planeand the context identifier of the UE comprises: obtaining, by the targetcontrol plane device, the context of the UE from a database by using theidentifier of the source control plane and the context identifier of theUE as index information.
 10. The method according to claim 7, whereinthe method further comprises: determining, by the target control planedevice, whether a forwarding plane gateway needs to change; and when theforwarding plane gateway needs to change, sending, by the target controlplane device, a source forwarding plane change flag to the target basestation, wherein the source forwarding plane change flag is used totrigger release of resources of a source side device.
 11. The methodaccording to claim 7, wherein the control plane device comprises amobility management entity or a centralized control plane device.
 12. Abase station, comprising: a processor, configured to obtain anidentifier of a source control plane and a context identifier of a UEfrom a source base station; and a transmitter, configured to send theidentifier of the source control plane and the context identifier of theUE to a target control plane device, wherein the identifier of thesource control plane and the context identifier of the UE are used toobtain a context of the UE.
 13. The base station according to claim 12,wherein the processor is configured to automatically establish aconnection between the target base station and the source base station,and obtain the identifier of the source control plane and the contextidentifier of the UE by using the source base station.
 14. The basestation according to claim 12, wherein the processor is furtherconfigured to: determine, based on the identifier of the source controlplane, whether the target base station is connected to the sourcecontrol plane; and when the target base station is not connected to thesource control plane, select a control plane as a target control plane.15. The base station according to claim 12, wherein the processor isfurther configured to trigger release of resources of a source sidedevice.
 16. The base station according to claim 15, wherein theprocessor is configured to control the transmitter to: when a sourceforwarding plane change flag sent by the target control plane isreceived, send a resource release message to the source base station,wherein the resource release message carries a source forwarding planegateway change flag.